Revolt is the most Discord-like FOSS chat app; it's very easy to use and customizable. Rocket.chat and Mattermost do similar things and are more oriented toward organizations (the Slack/Teams Classic use case).
Matrix is missing the entire voice chat, video chat, and streaming aspect of Discord.
It has meetings and calls, but those are much less convenient to use compared to persistent voice channels, and the streaming had a lot of latency when I tried it last.
Thanks for sharing. Anything in particular that was broken, or just a bad experience overall? I thought about spinning it up for family group video chats, but I guess I can cross that one off the list.